When a vehicle driver receives glaring light radiated from the headlights of an oncoming vehicle at night, it is a general practice to notify the driver of the oncoming vehicle of the fact by blinking the headlights to prompt him or her to reduce the intensity of the headlights through a change in the illumination mode, for example, from high beam to low beam. However, it depends on the mind of the driver of the oncoming vehicle whether the intensity of the headlights is reduced or not. Therefore, if the driver of the oncoming vehicle is bad-mannered, the headlight intensity will not be properly reduced even if the driver is so prompted. Thus, the driver may be dazzled by the light radiated from the headlights of the oncoming vehicle, and the field of view of the vehicle may consequently be obscured.
JP 2001-26236A (Document 1), for example, proposes a vehicle control apparatus. When a vehicle and another vehicle behind the same are equipped with this control apparatus, the quantity of light from the headlights of the trailing vehicle is detected by the subject vehicle (the leading vehicle preceding the trailing vehicle in this case), and the distance between the vehicles is detected at the trailing vehicle. When the quantity of light from the headlights of the trailing vehicle exceeds a predetermined quantity, the control apparatus of the leading vehicle transmits a control signal indicating the fact to the control apparatus of the trailing vehicle. When the vehicle distance falls below a predetermined value and the control signal is also received, the control apparatus of the trailing vehicle exercises control for reducing the intensity of the headlights or changing the angle of radiation. Therefore, a desirable field of view can be maintained at a subject (controlled) vehicle without any special operation where vehicles carry such control apparatus.
U.S. Pat. No. 6,861,809 proposes another vehicle light control apparatus. This vehicle light control apparatus exercises light distribution control for automatically switching the vehicle carrying the apparatus from high beam to low beam when it detects the tail lights of a leading vehicle or the headlights of the oncoming vehicle.
A subject vehicle will have many leading vehicles and oncoming vehicles on a road having heavy traffic, and the above vehicle light control apparatuses may not be able to maintain a sufficient field of view at the subject vehicle in such cases as exemplified below.
First, the vehicle light control apparatus disclosed in Document 1 indiscriminately transmits the control signal to the control apparatus of all vehicles concerned even when, for example, the quantity of light from only one of the plurality of vehicles is excessive. It is not possible to request only the vehicle having the excessive quantity of light to reduce the intensity of light. The vehicle light control apparatus disclosed in Document 2 only controls the light distribution of the subject vehicle (reduces the intensity of the lights) by detecting a leading vehicle or oncoming vehicle. In this case, the problem of an insufficient field of view at the subject vehicle cannot be solved, unless an illumination adjusting process such as reducing light intensity is carried out at the other vehicle. As thus described, either of the vehicle light control apparatus has not been able to sufficiently mitigate the problem of an insufficient field of view at a subject vehicle caused by an illumination adjustment failure such as an excessive quantity of light or a light distribution failure at another vehicle running near the same.